Philippines President Rodrigo Duterte visits the newly inaugurated Japan's built patrol ship during the ceremony marking the anniversary of the Philippines Coast Guard in Manila, Philippines, October 12, 2016.Damir Sagolj

MANILA (Reuters) - Philippine leader Rodrigo Duterte called U.S. President Barack Obama, the European Union and United Nations "fools" on Thursday, and warned they would end up humiliated and outsmarted if they accepted an invitation to investigate his war on drugs.

Duterte said he was open to an outside probe by Obama, his Secretary of State John Kerry, the EU and the U.N. Commission on Human Rights into alleged extrajudicial killings, but on the condition that after he was questioned, he had the right to be heard.

"I'll play with you. I'm very sure they cannot be brighter than me. I will ask five questions that will humiliate you," Duterte said. "Watch out for that, it will be a spectacle."

Duterte's remarks came during a televised speech to hundreds of the country's business elite, during which he said it was necessary to cleanse the streets of drug pushers and rescue the next generation of Filipinos from the scourge of narcotics.

Duterte, 71, won the hearts of millions of Filipinos with his outrageous, at times comical speeches and man-of-the-people style in the run-up to a May election. He won by a huge margin after campaigning almost entirely on promises to wipe out drugs and crime.

Nearly 2,300 people have died in the war on drugs since the campaign started on June 30, according to police, of which 1,566 were drug suspects killed in police operations.

Police had previously said there had been more then 3,600 deaths, but have since concluded that many of that number were homicides and murders unrelated to illegal narcotics.

Opinion polls for Duterte's first 90 days in office suggest he remains popular, with a Pulse Asia survey on Wednesday showing he had the trust of 86 percent of 1,200 Filipinos surveyed.

Duterte said on Wednesday he had officially invited a United Nations special rapporteur on extrajudicial executions to investigate the drug killings.

Thursday speech was the latest among Duterte's frequent and furious rebukes of international critics of his drugs war, after they expressed concern about the unusually high death toll and circumstances of the drugs killings.

"These fools think (they can do anything) because the Philippines is a small nation," he said. "Maybe God gave you the money but we have the brains."